The present invention is an improved piston for use in internal combustion engines, especially of the diesel type. Of all engine components, the piston is one of the most severely loaded, both mechanically and thermally. In the design of a more durable engine, it is therefore desirable to provide a piston which incorporates an improved means for cooling the piston head without sacrificing the strength needed to endure the high mechanical stresses incident to combustion. It is also desirable to provide an economical yet reliable design from a manufacturing standpoint.
Pistons have been designed in the past to provide a cooling fluid to the underside of the piston head, thus partially relieving the problem of thermal stress. One such design is that disclosed in U.S. Pat. No. 3,336,844 to Cornet, in which a multi-component piston is provided with an interior fluid-carrying trough. The trough collects, for recycling, oil which has been scraped from the cylinder wall during operation of the engine. While some incidental cooling is said to be achieved by oil splashing up from the trough against the interior crown surface, sufficient oil could not be obtained from the cylinder wall for cooling a piston of a modern high output diesel engine.
Similarly, the Maybach et al. U.S. Pat. No. 2,759,461 and the Athenstaedt U.S. Pat. No. 3,930,472 disclose a labyrinth of oil-carrying channels and conduits in two-piece pistons. However the design is impractical and complicated and could not be used in a piston having a relatively short piston pin to crown dimension.
The Clary et al. U.S. Pat. No. 3,805,677 discloses a two-piece piston provided with a transverse bridge member spanning the skirt section. The bridge member is of a material having a coefficient of thermal expansion less than that of the material of which the head and skirt portions are formed, in order to restrict the amount of thermal expansion of the skirt, thereby enabling a reduction in the noise generated and in the rate of cavitation erosion. The bridge member also provides the strength required to resist the side thrust loads at the top of the skirt. The bridge member is provided with one or more apertures to enable cooling oil to enter the chamber between the bridge and the central undercrown surface of the head, but there is no peripheral coolant chamber for cooling the peripheral undercrown portion of the head.
The present invention overcomes these disadvantages by providing a generally annular interior oil-carrying cavity adjacent the periphery of the piston crown. The cavity is defined by opposed portions of two integral piston sections thereby simplifying manufacturing techniques and increasing reliability and durability of the assembled unit.